Micro electric machine system resonator, drive method thereof, manufacturing method thereof, and frequency filter

ABSTRACT

The phases of outputs are made different by 180° to allow unbalanced inputs to be output as balanced outputs.  
     A MEMS resonator ( 101 ) has an input electrode ( 111 ) for inputting a signal, output electrodes (first output electrode ( 112 ), second output electrode ( 113 )) for outputting balanced output signals from unbalanced input signals, and an oscillator facing the input electrode ( 111 ), first output electrode ( 112 ) and second output electrode ( 113 ) via a space ( 121 ), wherein the first output electrode ( 112 ) is disposed at a position having a phase different by 180° from the phase of the input electrode ( 111 ) and the second output electrode ( 113 ) is disposed at a position having the same phase as that of the input electrode ( 111 ).

TECHNICAL FIELD

The present invention relates to a resonator of microelectromechanicalsystems easily outputs balanced signals, its driving method and afrequency filter.

BACKGROUND ART

With the development of information communication technologies, thenumber of devices utilizing networks has recently increased rapidly, andthere are high demands for wireless network technologies from thestandpoint of usage convenience.

An RF (radio frequency) front end module used in wireless communicationshas a semiconductor chip as well as relatively large size componentssuch as an RF filter, a surface acoustic wave (SAW) filter and adielectric filter for an IF (intermediate frequency) filter. Theexistence of these components has hindered compactness and low cost ofan RF front end. A present demand is to incorporate these filterfunctions into a semiconductor chip.

Research institutes including the University of Michigan have proposedto use a micro oscillator formed by utilizing semiconductor processes asan IF (intermediate frequency) filter and an RF (radio frequency) filteramong wireless communication devices, because the micro oscillator hascharacteristics such as having a small device occupying area, being ableto realize a high Q value, and being able to be integrated with othersemiconductor devices (for example, refer to Non-Patent Document 1(“High-Q HF Microelectromechanical Filters” by Frank D. Bonnon III, etal, IEEE (The Institute of Electrical and Electronics Engineers) JOURNALOF SOLID-STATE CIRCUITS, VOL. 35, NO. 4 Apr., 2000, p. 512-526). Atypical example of this structure will be described with reference to anoutline structure cross sectional view of FIG. 18.

As shown in FIG. 18, a micro oscillator 301 has the following structure.An oscillator electrode 312 is disposed above an output electrode 311mounted on a substrate 310 with a space 321 being involved. Theoscillator electrode 312 is connected to an input electrode 514 via anelectrode 313.

Next, the operation of the micro oscillator will be described below. Asa voltage at a specific frequency is applied to the input electrode 313,a beam (oscillation portion) of the oscillator electrode 312 mountedabove the output electrode 311 via the space 321 oscillates at acharacteristic frequency so that the capacitance of a capacitorconstituted of the space between the output electrode 311 and beam(oscillation portion) changes, and this change is output as a voltagefrom the output electrode 311 (for example, refer to Non-Patent Document1).

However, resonance frequencies of micro oscillators proposed andverified heretofore do not exceed 200 MHz at a maximum, and it isdifficult to provide a filter of a GHz range by conventional surfaceacoustic waves (SAW) or thin film acoustic waves (FBAR), with a high Qvalue characteristic to micro oscillators in a GHz band frequency range.

Presently, there is a tendency that a resonance peak of an output signalin a high frequency range becomes generally small. In order to obtaingood filter characteristics, it is necessary to improve an SN ratio ofthe resonance peak. According to the document (an example of a Disktype) of the University of Michigan (for example, refer to Non-PatentDocument 1), noise components in an output signal are generated by asignal directly passing through a parasitic capacitor formed betweeninput/output electrodes, and in order to reduce this signal, anoscillator electrode applied with a direct current (DC) is disposedbetween input and output electrodes to thereby reduce the noisecomponents.

In order to obtain a sufficient output signal of a Disk type oscillator,a DC voltage over 30 V is required so that a practical structure isdesired to be a beam type structure using a doubly-supported beam. Ifthe noise component reduction method is adopted to the beam typestructure, the electrode layout such as shown in FIG. 19 is used.

As shown in FIG. 19, on a substrate 410 having a laminated film of asilicon oxide film and a silicon nitride film formed on a siliconsubstrate, an input electrode 411 and an output electrode 412 aredisposed in parallel and spaced a part from each other. Above the inputand output electrodes, a beam type oscillator 413 is disposed traversingthe input and output electrodes 411 and 412 with a small space 421 beinginterposed therebetween. A curve shown in the drawing is an oscillationcurve of the beam type oscillator 413.

The oscillator 413 of the resonator of this type provides secondary modeoscillations, unbalanced input and unbalanced outputs. If the resonatorof this type is used for a balanced input frequency filter, as shown inFIG. 20 it is necessary to connect a balun device 531 that changesoutput signals (balanced inputs) from a previous stage device (e.g., anintegrated circuit) 521 to unbalanced inputs for a frequency filter 511and a balun device 532 that is connected at an output stage of thefrequency filter 511 and changes unbalanced outputs from the frequencyfilter 511 to balanced outputs. In this manner, a balanced input signalcan be input to a subsequent stage device (e.g., an integrated circuit)522 connected to the frequency filter 511.

A problem to be solved resides in that outputs of a conventionalresonator in microelectromechanical systems (hereinafter described as anMEMS resonator) are unbalanced. Moreover, a frequency filter using aresonator with unbalanced inputs and balanced outputs is needed forpractical usage. If outputs are unbalanced, a balun device for changingunbalance to balance is required additionally.

A conventional resonator in microelectromechanical systems is a devicewith unbalanced inputs and unbalanced outputs. The main trend in presentcommunication apparatus is balanced signals in an integrated circuit. Inorder to use a conventional MEMS resonator, for example, abalance-unbalance (Balun) converter is required for the application toIF filters or the like. This means an increase in cost and size,resulting in difficulty of adopting MEMS resonators.

DISCLOSURE OF THE INVENTION

In a resonator in a microelectromechanical having: an input electrodefor inputting a signal; an output electrode for outputting a signal; andan oscillator facing the input electrode and the output electrode via aspace, the most important characteristic of the resonator in amicroelectromechanical system of the present invention is that theoutput electrode has an electrode for outputting a balanced signal.

In a manufacture method for a resonator in a microelectromechanicalsystem, the resonator having: input electrodes for inputting signals;output electrodes for outputting signals; and an oscillator facing theinput electrodes and the output electrodes via a space, the mostimportant characteristic of the manufacture method for a resonator in amicroelectromechanical system of the present invention is to include thesteps of: forming the input electrodes and the output electrodes at thesame time; forming a first input electrode and a second input electrodeas the input electrodes; forming a first output electrode and a secondoutput electrode as the output electrodes; disposing the first inputelectrode and the first output electrode in such a manner that amplitudephases of the oscillator at positions of the first input electrode andthe first output electrode become a same phase; and disposing and thesecond input electrode and the second output electrode in such a mannerthat amplitude phases of the oscillator at positions of the second inputelectrode and the second output electrode become a same phase anddifferent by 180° from the phase of the oscillator.

In a driving method for a resonator in a microelectromechanical system,the resonator having: an input electrode for inputting a signal; outputelectrodes for outputting signals; and an oscillator facing the inputelectrode and the output electrodes via a space, the most importantcharacteristic of the driving method for a resonator in amicroelectromechanical system of the present invention is thatunbalanced signals are input and balanced signals are output.

In a resonator in a microelectromechanical system, the resonator having:an input electrode for inputting a signal; output electrodes foroutputting signals; and an oscillator facing the input electrode and theoutput electrodes via a space, the most important characteristic of afrequency filter of the present invention is that the resonator has theoutput electrodes including electrodes for inputting unbalanced signalsand outputting balanced signals.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an outline structure cross sectional view showing a firstembodiment of a MEMS resonator of the present invention.

FIG. 2 is an oscillation curve showing an oscillation mode of anoscillator of the MEMS resonator shown in FIG. 1.

FIGS. 3A to 3H are manufacture process cross sectional viewsillustrating an example of a manufacture method for a MEMS resonator ofthe present invention.

FIG. 4 is an outline structure circuit diagram using a filter of thepresent invention.

FIG. 5 is an outline structure cross sectional view showing a secondembodiment of a MEMS resonator of the present invention.

FIG. 6 is an oscillation curve showing an oscillation mode of anoscillator of the MEMS resonator shown in FIG. 5.

FIG. 7 is a manufacture process cross sectional view illustrating anexample of a manufacture method for the MEMS resonator of the secondembodiment.

FIG. 8 is an outline structure cross sectional view showing a thirdembodiment of a MEMS resonator of the present invention.

FIG. 9 is an oscillation curve showing an oscillation mode of anoscillator of the MEMS resonator shown in FIG. 8.

FIG. 10 is a manufacture process cross sectional view illustrating anexample of a manufacture method for the MEMS resonator of the thirdembodiment.

FIGS. 11A and 11B are outline structure cross sectional views showing afourth embodiment of a MEMS resonator of the present invention.

FIG. 12 is an oscillation curve showing an oscillation mode of anoscillator of the MEMS resonator shown in FIG. 11A.

FIGS. 13A and 13B are outline structure cross sectional views showing afifth embodiment of a MEMS resonator of the present invention.

FIG. 14 is an oscillation curve showing an oscillation mode of anoscillator of the MEMS resonator shown in FIG. 13A.

FIG. 15 is an outline structure cross sectional view showing a sixthembodiment of a MEMS resonator of the present invention.

FIGS. 16A to 16H are manufacture process cross sectional viewsillustrating an example of a manufacture method for a MEMS resonator ofthe present invention.

FIG. 17 is a block diagram illustrating inputs and outputs of a filterof the present invention.

FIG. 18 is an outline structure cross sectional view of a conventionalMEMS resonator.

FIG. 19 is an outline structure cross sectional view of a conventionalMEMS resonator.

FIG. 20 is a block diagram illustrating inputs and outputs of a filterusing a conventional MEMS resonator.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

The first embodiment of a MEMS resonator 101 of the present inventionwill be described with reference to the outline structure crosssectional view of FIG. 1.

As shown in FIG. 1, on a substrate 110 having an insulating film (notshown) formed on the surface thereof, an input electrode 111 forinputting a signal, a first output electrode 112 and a second outputelectrode 113 for outputting signals are formed in parallel. Inaddition, the first output electrode 112 is disposed at a positionhaving a phase different by 180° from that of the input electrode 111,whereas the second output electrode 113 is disposed at a position havingthe same phase as that of the input electrode 111. Further, electrodes134 of the resonator are disposed sandwiching the input electrode 111,first output electrode 112 and second output electrode 113. Anoscillator 114 is formed above the input electrode 111, first outputelectrode 112 and second output electrode 113, facing these electrodesvia a space 121 and being connected to the electrodes 134. The space 121is formed having a distance of, for example, about 0.1 μm between theoscillator 114 and the input electrode 111, first output electrode 112and second output electrode 113.

The oscillator 114 of the MEMS resonator 101 constructed as aboveoscillates in a third-order mode drawing an oscillation curve such asshown in FIG. 2. Therefore, the MEMS resonator 101 outputs a combinedoutput of an output Out1 from the first output electrode 112 and anoutput Out2 from the second output electrode 113 having a phasedifferent by 180° from that of the first output electrode 112, so thatunbalanced outputs can be changed to balanced outputs.

Next, an example of a manufacture method for the MEMS resonator 101 ofthe present invention will be described with reference to themanufacture process cross sectional views shown in FIGS. 3A to 3H.

As shown in FIG. 3A, an insulating film 132 is formed on a semiconductorsubstrate 131. For example, the semiconductor substrate 131 is a siliconsubstrate and the insulating film 132 is a silicon nitride (SiN) film.The silicon nitride film has a thickness of, for example, 1 μm. Insteadof the silicon nitride film, a laminated film of a silicon oxide filmand a silicon nitride film may be used. In this manner, a substrate 110is constituted of, for example, a silicon substrate as the semiconductorsubstrate 131 and the insulating film 132 formed on the semiconductorsubstrate. An electrode forming film 133 is formed on the insulatingfilm 132. For example, the electrode forming film 133 is made of apolysilicon film and has a thickness of 0.5 μm.

Next, as shown in FIG. 3B, the electrode forming film 133 is processedinto the forms of the input electrode and output electrodes by resistcoating and lithography techniques to form a resist mask, andthereafter, by using the resist mask, the electrode forming film 133 isetched to form the input electrode 111, first output electrode 112 andsecond output electrode 113. At the same time, the oscillator electrodes134 are formed from the electrode forming film 133. In this case, thefirst output electrode 112 is disposed at a position having a phasedifferent by 180° from that of the input electrode 111, whereas thesecond output electrode 113 is disposed at a position having the samephase as that of the input electrode 111. Further, the oscillatorelectrodes 134 are formed sandwiching an electrode group including theinput electrode 111, first output electrode 112 and second outputelectrode 113, and being spaced from the electrode group.

Next, as shown in FIG. 3C, a sacrificial layer 135 thicker than theinput electrode 111 and output electrode 112 is formed covering theinput electrode 111, first output electrode 112, second output electrode113 and oscillator electrodes 134. For example, the sacrificial layer135 is a silicon oxide film and has a thickness of 0.5 μm. It issufficient if the sacrificial layer 135 is made of material which isselectively etched relative to the insulating film 132 and electrodes.

Next, as shown in FIG. 3D, the surface of the sacrificial layer 135 isplanarized by chemical mechanical polishing. At this time, thesacrificial layer 135 is left thin on the input electrode 111, firstoutput electrode 112 and second output electrode 113. Since a thicknessto be left determines a distance between an oscillator to be formedlater and the input electrode 111, first output electrode 112 and secondoutput electrode 113, the sacrificial layer 135 corresponding to thedistance is to be left. For example, the sacrificial layer 135 having athickness of 0.1 μm is left on the input electrode 111, first outputelectrode 112 and second output electrode 113.

Next, as shown in FIG. 3E, an etching mask is formed by ordinary resistcoating and lithograph techniques, and by using the etching mask, thesacrificial layer 135 is partially etched to form openings 136 exposingpartial surfaces of the electrodes 134.

Next, as shown in FIG. 3F, an oscillator forming film 137 is formed onthe whole surface of the sacrificial layer 135. For example, theoscillator forming film 137 is a polysilicon film and has a thickness of0.5 μm.

Next, as shown in FIG. 3G, an etching mask is formed by ordinary resistcoating and lithograph techniques, and by using the etching mask, theoscillator forming film 137 is etched to form a beam-like oscillator114. The oscillator 114 is connected to the electrodes 134 via theopenings 136.

Next, as shown in FIG. 3H, the sacrificial layer 135 (refer to FIG. 3G)is etched and removed by wet etching. Since the sacrificial layer 135 ismade of silicon oxide in this example, hydrofluoric acid is used.Therefore, a space 121 is formed on both sides of each of the inputelectrode 111, first output electrode 112 and second output electrodes113, and between the oscillator 114 and the input electrode 111, firstoutput electrode 112 and second output electrodes 113. The space 121 hasa distance of about 0.1 μm between the oscillator 114 and the inputelectrode 111, first output electrode 112 and second output electrodes113. In this manner, the MEMS resonator 101 is formed.

A method of forming each film by the above-described manufacture methodmay adopt CVD, sputtering, evaporation and the like. A thickness of eachfilm is designed appropriately. If the uppermost surface of theinsulating film 132 is made of silicon oxide and each electrode is madeof polysilicon, the sacrificial layer 135 may be made of siliconnitride. In this case, hot phosphoric acid is used for wet-etching thesacrificial layer 135.

With the above-described manufacture method, the MEMS resonator 101 ofthe third-order mode capable of outputting balanced outputs fromunbalanced inputs can be obtained.

Next, an embodiment using the MEMS resonator 101 of the presentinvention as a frequency filter will be described with reference to theoutline structure circuit diagram shown in FIG. 4.

As described earlier, the MEMS resonator 101 of the present inventionoutputs balanced outputs from unbalanced inputs. Therefore, if theresonator 101 is used as the frequency filter, it is not necessary touse the balun device for changing unbalanced inputs to balanced outputs.More specifically, as shown in FIG. 4, a frequency filter 171 using theMEMS resonator 101 of the present invention outputs balanced outputsfrom unbalanced inputs. It is therefore possible to directly connect aprevious stage integrated circuit 181 to the frequency filter 171.

Second Embodiment

The second embodiment of a MEMS resonator of the present invention willbe described with reference to the outline structure cross sectionalview of FIG. 5. The MEMS resonator has a first output electrode disposedon both sides of the second output electrode.

As shown in FIG. 5, on a substrate 110 having an insulating film (notshown) formed on the surface thereof, an input electrode 111 forinputting a signal, a first output electrode 112 (1121), a second outputelectrode 113 and a first output electrode 112 (1122) for outputtingsignals are formed in parallel. In addition, the first output electrodes112 are disposed at positions having a phase different by 180° from thatof the input electrode 111, whereas the second output electrode 113 isdisposed at a position having the same phase as that of the inputelectrode 111 and between the first output electrodes 1121 and 1122.Further, electrodes 134 of the resonator are disposed sandwiching theinput electrode 111, first output electrodes 112 and second outputelectrode 113. An oscillator 114 is formed above the input electrode111, first output electrodes 112 and second output electrode 113, facingthese electrodes via a space 121 and being connected to the electrodes134. The space 121 is formed having a distance of, for example, about0.1 μm between the oscillator 114 and the input electrode 111, firstoutput electrodes 112 and second output electrode 113.

The oscillator 114 of the MEMS resonator 102 constructed as aboveoscillates in a fourth-order mode drawing an oscillation curve such asshown in FIG. 6. Therefore, the MEMS resonator 102 outputs a combinedoutput of outputs Out1 from the first output electrodes 112 (1121 and1122) and an output Out2 from the second output electrode 113 having aphase different by 180° from that of the first output electrodes 112, sothat unbalanced outputs can be changed to balanced outputs.

For a manufacture method for the MEMS resonator 2, in the manufacturemethod described with reference to FIGS. 3A to 3H, an electrode formingfilm 133 is patterned in such a manner that the input electrode 111,first output electrode 1121, second output electrode 113 and firstoutput electrode 122 are formed in parallel in this order as shown inFIG. 7. More specifically, the first output electrodes 1121 and 1122 aredisposed at positions having a phase different by 180° from that of theinput electrode 111, and the second output electrode 113 is disposed ata position having the same phase as that of the input electrode 111.Further, the second output electrode 113 is disposed between the firstoutput electrodes 1121 and 1122. Furthermore, the oscillator electrodes134 are formed sandwiching an electrode group including the inputelectrode 111, first output electrodes 1121 and 1122 and second outputelectrode 113. Other processes are similar to those of the manufacturemethod described with reference to FIGS. 3A to 3H.

Third Embodiment

The third embodiment of a MEMS resonator of the present invention willbe described with reference to the outline structure cross sectionalview of FIG. 8. The MEMS resonator has an input electrode and a firstoutput electrode disposed alternately.

As shown in FIG. 8, on a substrate 110 having an insulating film (notshown) formed on the surface thereof, an input electrode 111 (1111) forinputting a signal, a first output electrode 112 (1121) for outputting asignal, an input electrode 111 (1112) for inputting a signal having thesame phase as that of the input electrode 1111, a first output electrode112 (1122) for outputting a signal and a second output electrode 113 areformed in parallel in this order. In addition, the first outputelectrodes 112 are disposed at positions having a phase different by180° from that of the input electrode 111, the input electrodes 1111 and1112 and first output electrodes 1121 and 1122 are disposed alternately,and the second output electrode 113 is disposed on the opposite side ofthe input electrode 111 relative to the first output electrode 112(1122) disposed at the last end of the layout of the input electrodes111 and first output electrodes 112, and at a position having the samephase as that of the input electrode 111. Further, electrodes 134 of theresonator are formed sandwiching the input electrodes 111, first outputelectrodes 112 and second output electrode 113. An oscillator 114 isformed above the input electrodes 111, first output electrodes 112 andsecond output electrode 113, facing these electrodes via a space 121 andbeing connected to the electrodes 134. The space 121 is formed having adistance of, for example, about 0.1 μm between the oscillator 114 andthe input electrodes 111, first output electrodes 112 and second outputelectrode 113.

The oscillator 114 of the MEMS resonator 103 constructed as aboveoscillates in a fifth-order mode drawing an oscillation curve such asshown in FIG. 10. Therefore, the resonator 103 outputs a combined outputof outputs Out1 from the first output electrodes 112 (1121 and 1122) andan output Out2 from the second output electrode 113 having a phasedifferent by 180° from that of the first output electrodes 112, so thatunbalanced outputs can be changed to balanced outputs.

For a manufacture method for the MEMS resonator 103, in the manufacturemethod described with reference to FIGS. 3A to 3H, an electrode formingfilm 133 is patterned in such a manner that the input electrode 1111,first output electrode 1121, input electrode 1112, first outputelectrode 1122 and second electrode 113 are formed in parallel in thisorder as shown in FIG. 10. More specifically, the input electrodes 1111and 1112 are disposed at positions having the same phase, the firstoutput electrodes 1121 and 1122 are disposed at positions having a phasedifferent by 180° from that of the input electrodes 1111 and 1112, theinput electrodes 1111 and 1112 and the first output electrodes 1121 and1122 are disposed alternately, and the second output electrode 113 isdisposed on the opposite side of the input electrode 1112 relative tothe first output electrode 1122 disposed at the last end of the layoutof the input electrodes 1111 and 1112 and first output electrodes 1121and 1122, and at a position having the same phase as that of the inputelectrodes 1111 and 1112. Furthermore, the oscillator electrode 134 isformed sandwiching an electrode group including the input electrode 1111and 1112, first output electrodes 1121 and 1122 and second outputelectrode 113. Other processes are similar to those of the manufacturemethod described with reference to FIGS. 3A to 3H.

Similar to the MEMS resonator 101, the MEMS resonators 102 and 103 canalso be used as the frequency filter described with reference to FIG. 4.

In the first to third embodiments described above, each of the inputelectrode 111, first output electrode 112, second output electrode 113,electrodes 134 may be made of metal instead of polysilicon. For example,the metal may use material used as metal wirings of a semiconductordevice, such as aluminum, gold, copper and tungsten.

In the resonator and its driving method in microelectromechanicalsystems of the present invention, since the output electrodes areprovided which can output balanced outputs from unbalanced inputs,unbalanced inputs and balanced outputs are possible. Accordingly, thefrequency filter of the present invention does not require the balundevice which is required for an RF filter using a conventional beam typeresonator. It is advantageous in that the circuit can be simplified andmade compact at low cost.

In the first to third embodiments, the object of outputting balancedoutputs from unbalanced inputs is realized by providing the electrodesof balanced outputs without using the balun device.

Fourth Embodiment

The fourth embodiment of a MEMS resonator 201 of the present inventionwill be described with reference to the outline structure crosssectional view of FIG. 11A and a plan layout diagram of FIG. 11B.

As shown in FIGS. 11A and 11B, on a substrate 210 having an insulatingfilm 252 formed on the surface thereof, a first input electrode 211 anda second input electrode 212 for inputting balanced signals and a firstoutput electrode 221 and a first output electrode 221 for outputtingbalanced signals are disposed in parallel in the order of the firstinput electrode 211, second output electrode 222, first output electrode221 and first input electrode 212, and at such positions as theamplitude phases of an oscillator 231 to be described later at thepositions of the first input electrode 211 and first output electrode221 become the same phase and the amplitude phases of the oscillator 231at the positions of the second input electrode 212 and second outputelectrode 222 become the same phase and different by 180° from that ofthe oscillator 231 at the position of the first input electrode 211.

Electrodes 233 and 234 of the resonator are formed sandwiching the firstinput electrode 211, second output electrode 222, first output electrode221 and second input electrode 212. The oscillator 231 is formed abovethe first input electrode 211, second output electrode 222, first outputelectrode 221 and second input electrode 212, facing these electrodesvia a space 241 and being connected to the electrodes 233 and 234. Thespace 241 is formed having a distance of, for example, about 0.1 μmbetween the oscillator 231 and the first input electrode 211, secondoutput electrode 222, first output electrode 221 and second inputelectrode 212.

The oscillator 231 of the MEMS resonator 201 constructed as aboveoscillates in a third-order mode drawing an oscillation curve such asshown in FIG. 12. Therefore, the MEMS resonator 201 inputs a balancedsignal from an input In1 to the first input electrode 211, and the inputsignal is output as a balanced signal from the first output electrode221 to an output Out1. Similarly, a balanced signal is input from aninput In2 to the second input electrode 212, and the input signal isoutput as a balanced signal from the second output electrode 222 to anoutput Out2. In this manner, a balanced input signal is output as abalanced output signal.

Fifth Embodiment

The fifth embodiment of a MEMS resonator 202 of the present inventionwill be described with reference to the outline structure crosssectional view of FIG. 13A and a plan layout diagram of FIG. 13B.

As shown in FIGS. 13A and 13B, on a substrate 210 having an insulatingfilm (not shown) formed on the surface thereof, a first input electrode211 and a second input electrode 212 for inputting balanced signals anda first output electrode 221 and a second output electrode 222 foroutputting balanced signals are disposed in parallel in the order of thefirst input electrode 211, second input electrode 212, first outputelectrode 221 and second output electrode 222, and at such positions asthe amplitude phases of an oscillator 231 to be described later at thepositions of the first input electrode 211 and first output electrode221 become the same phase and the amplitude phases of the oscillator 231at the positions of the second input electrode 212 and second outputelectrode 222 become the same phase and different by 180° from that ofthe oscillator 231 at the position of the first input electrode 211.

Electrodes 233 and 234 of the resonator are formed sandwiching the firstinput electrode 211, second input electrode 212, first output electrode221 and second output electrode 222. The oscillator 231 is formed abovethe first input electrode 211, second input electrode 212, first outputelectrode 221 and second output electrode 222, facing these electrodesvia a space 241 and being connected to the electrodes 233 and 234. Thespace 241 is formed having a distance of, for example, about 0.1 μmbetween the oscillator 231 and the first input electrode 211, secondoutput electrode 222, first output electrode 221 and second inputelectrode 212.

The oscillator 231 of the MEMS resonator 202 constructed as aboveoscillates in a third-order mode drawing an oscillation curve such asshown in FIG. 14. Therefore, the MEMS resonator 102 inputs a balancedsignal from an input In1 to the first input electrode 211, the inputsignal is output as a balanced signal from the first output electrode221 to an output Out1. Similarly, a balanced signal is input from aninput In2 to the second input electrode 212, and the input signal isoutput as a balanced signal from the second output electrode 222 to anoutput Out2. In this manner, a balanced input signal is output as abalanced output signal.

Sixth Embodiment

In the above-described fourth and fifth embodiments, the MEMS resonatorin the fourth-order mode has been described. The MEMS resonator of thepresent invention can be made to oscillate in a 2n-th order mode (n is anatural number of 2 or larger). For example, an example of a MEMSresonator capable of vibrating in the sixth-order mode will be describedwith reference to the outline structure cross sectional view of FIG. 15.

As shown in FIG. 15, on a substrate 210 having an insulating film (notshown) formed on the surface thereof, a first input electrode 211, asecond input electrode 212, a third input electrode 213 and a fourthinput electrode 214 for inputting balanced signals and a first outputelectrode 221 and second output electrode 222 for outputting balancedsignals are disposed in parallel in the order of the first inputelectrode 211, second input electrode 212, first output electrode 221,second output electrode 222, third input electrode 213 and fourth inputelectrode 214, and at such positions as the amplitude phases of anoscillator 231 to be described later at the positions of the first inputelectrode 211, first output electrode 221 and third input electrode 213become the same phase and the amplitude phases of the oscillator. 231 atthe positions of the second input electrode 212, second output electrode222 and fourth input electrode 214 become the same phase and differentby 180° from that of the oscillator 231 at the position of the firstinput electrode 211.

Electrodes 233 and 234 of the resonator are formed sandwiching the firstinput electrode 211, second input electrode 212, third input electrode213, fourth input electrode 214, first output electrode 221 and secondoutput electrode 222. The oscillator 231 is formed above the first inputelectrode 211, second input electrode 212, third input electrode 213,fourth input electrode 214, first output electrode 221 and second outputelectrode 222, facing these electrodes via a space 241 and beingconnected to the electrodes 233 and 234. The space 241 is formed havinga distance of, for example, about 0.1 μm between the oscillator 231 andthe first input electrode 211, first input electrode 211, first outputelectrode 221, second output electrode 222, third input electrode 213and fourth input electrode 214.

The oscillator 231 of the MEMS resonator 203 constructed as aboveoscillates in a sixth-order mode drawing an oscillation curve such asshown in FIG. 15. Therefore, the MEMS resonator 201 inputs a balancedsignal from an input In1 to the first input electrode 211 and thirdinput electrode 213, and the input signal is output as a balanced signalfrom the first output electrode 221 to an output Out1. Similarly, abalanced signal is input from an input In2 to the second input electrode212 and fourth input electrode 214, and the input signal is output as abalanced signal from the second output electrode 222 to an output Out2.In this manner, a balanced input signal is output as a balanced outputsignal.

The layout positions of each input electrode (first input electrode,second input electrode, third input electrode, . . . ) and each outputelectrode (first output electrode, second output electrode, third outputelectrode, . . . ) of the MEMS resonator in the 2n-th (n is a naturalnumber of 2 or larger) order oscillation mode are as follows.

The first input electrode is disposed at an odd number position among2n, and the first output electrode for outputting a signal input to thefirst input electrode is disposed at an odd number position among 2nother than the position where the first input electrode is disposed. Thesecond input electrode is disposed at an even number position among 2n,and the second output electrode for outputting a signal input to thesecond input electrode is disposed at an even number position among 2nother than the position where the second input electrode is disposed. Inthe case of the sixth-order mode or higher, an input electrode of thethird input electrode and subsequent input electrodes (third inputelectrode, fourth input electrode, . . . ) is disposed at a vacant oddnumber position among 2n if the input electrode has the same phase asthat of the first input electrode, or at a vacant even number positionamong 2n if the input electrode has the same phase as that of the secondinput electrode, and an output electrode of the third output electrodeand subsequent output electrodes (third output electrode, fourth outputelectrode, . . . ) is disposed at a vacant odd number position among 2nif the output electrode has the same phase as that of the first outputelectrode, or at a vacant even number position among 2n if the outputelectrode has the same phase as that of the second output electrode.

As described above, if each input electrode and each output electrodeare disposed in such a manner that a balanced signal is input to theinput electrode and the signal is output as a balanced signal from theoutput electrode, then the MEMS resonator of the present invention canbe made as a MEMS resonator of the 2n-th order (n is a natural number of2 or larger). Since the oscillator of the higher order mode MEMSresonator becomes long, the oscillator can be processed with highaccuracy. Informing a higher order mode MEMS resonator, it is necessaryto determine the number of input electrodes and output electrodes byconsidering durability of the oscillator and its mount portion.

Seventh Embodiment

Next, an example of a manufacture method for the MEMS resonator 201 ofthe present invention will be described with reference to themanufacture process cross sectional views shown in FIGS. 16A to 16H.

As shown in FIG. 16A, an insulating film 252 is formed on asemiconductor substrate 251. For example, the semiconductor substrate251 is a silicon substrate and the insulating film 252 is a siliconnitride (SiN) film. The silicon nitride film has a thickness of, forexample, 1 μm. Instead of the silicon nitride film, a laminated film ofa silicon oxide film and a silicon nitride film may be used. In thismanner, a substrate 210 is constituted of, for example, a siliconsubstrate as the semiconductor substrate 251 and the insulating film 252formed on the semiconductor substrate. An electrode forming film 253 isformed on the insulating film 252. For example, the electrode formingfilm 253 is made of a polysilicon film and has a thickness of 0.5 μm.

Next, as shown in FIG. 16B, a resist mask for processing the electrodeforming film 253 into the forms of the input electrodes and outputelectrodes is formed by resist coating and lithography techniques, andthereafter, by using the resist mask, the electrodes forming film 253(refer to FIG. 16A) is etched to form the first input electrode 211,second output electrode 222, first output electrode 221 and second inputelectrode 212. At the same time, the oscillator electrodes 233 and 234are formed from the electrode forming film 253 (refer to FIG. 16A). Inthis case, the first input electrode 211 and first output electrode 221are disposed at such positions as the amplitude phases of the oscillatorto be formed later at the positions of the first input electrode 211 andfirst output electrode 221 become the same phase, whereas the secondinput electrode 212 and second output electrode 222 are disposed at suchpositions as the amplitude phases of the oscillator to be formed laterat the positions of the second input electrode 212 and second outputelectrode 222 become the same phase and different by 180° from theamplitude phase of the oscillator to be formed later at the positionwhere the first input electrode 211 is formed. For example, the firstinput electrode 211, second output electrode 222, first output electrode221 and second input electrode 212 are formed in this order. Theoscillator electrodes 233 and 234 are formed sandwiching an electrodegroup including the first input electrode 211, second output electrode222, first output electrode 221 and second input electrode 212, andbeing spaced from the electrode group. It is sufficient if the layout ofthe first and second input electrodes 211 and 212 and first and secondoutput electrodes 221 and 222 allows a balanced input signal to be inputto each input electrode and a balanced output signal to be output fromeach output electrode.

Next, as shown in FIG. 16C, a sacrificial layer 254 thicker than thefirst and second input electrodes 211 and 212 and first and secondoutput electrodes 221 and 222 is formed covering the first inputelectrode 211, second output electrode 222, first output electrode 221,second input electrode 212 and oscillator electrode 234. For example,the sacrificial layer 254 is a silicon oxide film and has a thickness of0.5 μm. It is sufficient if the sacrificial layer 254 is made ofmaterial which is selectively etched relative to the insulating film 252and electrodes.

Next, as shown in FIG. 16D, the surface of the sacrificial layer 254 isplanarized by chemical mechanical polishing. At this time, thesacrificial layer 254 is left thin on the first and second inputelectrodes 211 and 212 and first and second output electrodes 221 and222. Since a thickness to be left determines a distance between anoscillator to be formed later and the first and second input electrodes211 and 212 and first and second output electrodes 221 and 222, thesacrificial layer 254 corresponding to the distance is to be left. Forexample, the sacrificial layer 254 having a thickness of 0.1 μm is lefton the first and second input electrodes 211 and 212 and first andsecond output electrodes 221 and 222. Similarly, the sacrificial layer254 is also left on the electrodes 233 and 234.

Next, as shown in FIG. 16E, an etching mask is formed by ordinary resistcoating and lithograph techniques, and by using the etching mask, thesacrificial layer 254 is partially etched to form openings 255 and 256exposing partial surfaces of the electrodes 233 and 234.

Next, as shown in FIG. 16F, an oscillator forming film 257 is formed onthe whole surface of the sacrificial layer 254. For example, theoscillator forming film 257 is a polysilicon film and has a thickness of0.5 μm.

Next, as shown in FIG. 16G, an etching mask is formed by ordinary resistcoating and lithograph techniques, and by using the etching mask, theoscillator forming film 257 is etched to form a beam-like oscillator231. The oscillator 231 is connected to the electrodes 233 and 234 viathe openings 255 and 256.

Next, as shown in FIG. 16H, the sacrificial layer 254 (refer to FIG.16G) is etched and removed by wet etching. Since the sacrificial layer254 is made of silicon oxide in this example, hydrofluoric acid is used.Therefore, a space 241 is formed on both sides of each of the firstinput electrode 211, second output electrode 222, first output electrode221 and second input electrodes 212, and between the oscillator 231 andthe first input electrode 211, second output electrode 222, first outputelectrode 221 and second input electrodes 212. The space 241 has adistance of about 0.1 μm between the oscillator 231 and the first inputelectrode 211, second output electrode 222, first output electrode 221and second input electrodes 212. In this manner, the MEMS resonator 201is formed.

A method of forming each film by the above-described manufacture methodmay adopt CVD, sputtering, evaporation and the like. A thickness of eachfilm is designed appropriately. If the uppermost surface of theinsulating film 252 is made of silicon oxide and each electrode is madeof polysilicon, the sacrificial layer 254 may be made of siliconnitride. In this case, hot phosphoric acid is used for wet-etching thesacrificial layer 254.

With the above-described manufacture method, the MEMS resonator 201 ofthe fourth-order mode capable of outputting balanced outputs fromunbalanced inputs can be obtained.

Eighth Embodiment

For a manufacture method for the MEMS resonator 202 of the presentinvention, in the MEMS resonator 201 manufacture method of the presentinvention described with reference to the manufacture process crosssectional views shown in FIGS. 16A to 16H, the first input electrode 211is used as the first input electrode, the second input electrode isformed at the position of the second output electrode 222, the firstoutput electrode 221 is used as the first output electrode, and thesecond output electrode is formed at the position of the second inputelectrode 212. Other processes are similar to those of the manufacturemethod described in the sixth embodiment.

Ninth Embodiment

Next, with reference to the block diagram shown in FIG. 17, descriptionwill be made on an embodiment wherein the MEMS resonator 1 or MEMSresonator 2 is used as a frequency filter.

As described above, the MEMS resonator 201 of the present inventionoutputs a balanced output from a balanced input. Therefore, if theresonator 201 is used as the frequency filter, it is not necessary touse the balun device for changing unbalanced outputs to balancedoutputs. More specifically, as shown in FIG. 17, by using the MEMSresonator 201 of the present invention as a frequency filter 271, outputsignals (balanced inputs) from a previous stage device (e.g., integratedcircuit) 281 are output as balanced outputs. It is therefore possible todirectly connect a subsequent stage device (e.g., integrated circuit)282 to the frequency filter 271.

Similar to the MEMS resonator 201, the MEMS resonators 202 and 203 canalso be used as the frequency filter described with reference to FIG.17.

In the fourth to ninth embodiments described above, each of the firstinput electrode 211, second input electrode 212, first output electrode221, second output electrode 222, electrode 234 and the like may be madeof metal instead of polysilicon. For example, the metal may use materialused as metal wirings of a semiconductor device, such as aluminum, gold,copper and tungsten.

In the MEMS resonators of the fourth to sixth embodiments of the presentinvention, since the input electrodes inputting balanced inputs and theoutput electrodes outputting balanced outputs are provided, balancedinputs and balanced outputs are possible. Accordingly, the frequencyfilter, particularly an RF filter and an IF filter, using the MEMSresonator of the present invention does not require the balun devicewhich is required for an RF filter or IF filter using a conventionalbeam type resonator. It is advantageous in that the circuit can besimplified and made compact at low cost.

In the manufacture method for the MEMS resonator of the seventh andeighth embodiments of the present invention descried above, the inputand output electrodes are formed at the same time, the first and secondinput electrodes are formed as the input electrodes, the first andsecond output electrodes are formed as the output electrodes, the firstinput electrode and first output electrode are disposed in such a mannerthat the amplitude phases of the oscillator at positions of the firstinput electrode and first output electrode become the same phase, andthe second input electrode and second output electrode are disposed insuch a manner that the amplitude phases of the oscillator at positionsof the second input electrode and second output electrode become thesame phase and different by 180° from that of the oscillator at theposition of the first input electrode. Accordingly, in the MEMSresonator, the balanced input to each input electrode can be output fromeach output electrode as the balanced output.

In the fourth to ninth embodiments, the object of outputting balancedoutputs from balanced inputs is realized by disposing at the same phasethe input electrode for inputting a balanced input signal and the outputelectrode for outputting a balanced output signal, without using thebalun device.

INDUSTRIAL APPLICABILITY

The resonator and its driving method in microelectromechanical systemsof the present invention are applicable to a frequency filter (RFfilter, IF filter, etc.), an oscillator and the like.

1. A MEMS resonator comprising: an input electrode for inputting asignal; an output electrode for outputting a signal; and an oscillatorfacing the input electrode and the output electrodes via a space, andthe MEMS resonator characterized in that the output electrode has anelectrode for outputting a balanced signal.
 2. A MEMS resonatorcomprising: an input electrode for inputting a signal; an outputelectrode for outputting a signal; and an oscillator facing the inputelectrode and the output electrode via a space, the MEMS resonatorcharacterized in that the output electrode has an electrode forinputting an unbalanced signal and outputting a balanced signal.
 3. TheMEMS resonator according to claim 2, characterized in that: the outputelectrode includes a first output electrode and a second outputelectrode disposed, on one side of the input electrode and spaced apartfrom each other; the first output electrode is disposed at a positionhaving a phase different by 180° from a phase of the input electrode;and the second output electrode is disposed at a position having a samephase as the phase of the input electrode.
 4. The MEMS resonatoraccording to claim 3, characterized in that: the first output electrodeis disposed on both sides of the second output electrode.
 5. The MEMSresonator according to claim 2, characterized in that: the outputelectrode includes a first output electrode and a second outputelectrode; the input electrode includes a plurality of input electrodes;the first output electrode is provided the same number as the number ofthe plurality of input electrodes, the first output electrodes and theplurality of input electrodes are disposed alternately, and at positionshaving phases different by 180° from a phase of each of the inputelectrodes; and the second output electrode is disposed at a positionopposite to the input electrode of the first output electrode disposedat a last end of a layout of the input electrodes and the first outputelectrodes, and at a position having a same phase as the phase of eachof the input electrodes.
 6. A MEMS resonator comprising: an inputelectrode for inputting a signal; an output electrode for outputting asignal; and an oscillator facing the input electrode and the outputelectrode via a space, the MEMS resonator in the microelectromechanicalsystem characterized in that: a balanced signal is input to the inputelectrode; and a balanced signal is output from the output electrode. 7.The MEMS resonator according to claim 6, characterized in that: theinput electrode includes a first input electrode and a second inputelectrode; the output electrode includes a first output electrode and asecond output electrode; the first input electrode and the first outputelectrode are disposed in such a manner that amplitude phases of theoscillator at positions of the first input electrode and the firstoutput electrode become a same phase; and the second input electrode andthe second output electrode are disposed in such a manner that amplitudephases of the oscillator at positions of the second input electrode andthe second output electrode become a same phase and different by 180°from the phase of the oscillator.
 8. The MEMS resonator according toclaim 7, characterized in that: the first input electrode, the secondoutput electrode, the first output electrode and the second inputelectrode are disposed in this order.
 9. The MEMS resonator according toclaim 7, characterized in that: the first input electrode, the secondinput electrode, the first output electrode and the second outputelectrode are disposed in this order.
 10. The MEMS resonator accordingto claim 6, characterized in that: the input electrode includes aplurality of input electrodes; the output electrode includes a pluralityof output electrodes; a first input electrode of the input electrodesand a first output electrode of the output electrodes are disposed insuch a manner that amplitude phases of the oscillator at positions ofthe first input electrode and the first output electrode become a samephase; a second input electrode of the input electrodes and a secondoutput electrode of the output electrodes are disposed in such a mannerthat amplitude phases of the oscillator at positions of the second inputelectrode and the second output electrode become a same phase anddifferent by 180° from the amplitude phases of the oscillator at aposition of the first input electrode; remaining input electrodes of theinput electrodes are disposed in such a manner that the remaining inputelectrodes have a same phase as an amplitude phase of the oscillator ata position of the first input electrode or the second input electrode;and remaining output electrodes of the output electrode are disposed insuch a manner that the remaining output electrodes have a same phase asan amplitude phase of the oscillator at a position of the first outputelectrode or the second output electrode.
 11. A driving method for aMEMS resonator, the MEMS resonator having: an input electrode forinputting a signal; an output electrode for outputting a signal; and anoscillator facing the input electrode and the output electrode via aspace, the driving method for the MEMS resonator in themicroelectromechanical system, characterized by comprising the step ofinputting an unbalanced signal and outputting a balanced signal.
 12. Thedriving method for a MEMS resonator according to claim 11, characterizedin that: the output electrode includes a first output electrode and asecond output electrode, disposed on one side of the input electrode andspaced apart from each other; the first output electrode is disposed ata position having a phase different by 180° from a phase of the inputelectrode; and the second output electrode is disposed at a positionhaving a same phase as the phase of the input electrode.
 13. The drivingmethod for a MEMS resonator according to claim 12, characterized inthat: the first output electrode is disposed on both sides of the secondoutput electrode.
 14. The driving method for a MEMS resonator accordingto claim 11, characterized in that: the output electrode includes afirst output electrode and a second output electrode; the inputelectrode includes a plurality of input electrodes; the first outputelectrode is provided the same number as the number of the plurality ofinput electrodes, the first output electrodes and the plurality of inputelectrodes are disposed alternately, and at positions having phasesdifferent by 180° from a phase of each of the input electrodes; and thesecond output electrode is disposed at a position opposite to the inputelectrode of the first output electrode disposed at a last end of alayout of the input electrodes and the first output electrode, and at aposition having a same phase as the phase of each of the inputelectrodes.
 15. A frequency filter characterized by comprising a MEMSresonator, the MEMS resonator having: an input electrode for inputting asignal; an output electrode for an outputting signal; and an oscillatorfacing the input electrode and the output electrode via a space, theMEMS resonator in the microelectromechanical system characterized inthat the output electrode has an electrode for inputting an unbalancedsignal and outputting a balanced signal.
 16. The frequency filteraccording to claim 15, characterized in that: the output electrodeincludes a first output electrode and a second output electrode,disposed on one side of the input electrode and spaced apart from eachother; the first output electrode is disposed at a position having aphase different by 180° from a phase of the input electrode; and thesecond output electrode is disposed at a position having a same phase asthe phase of the input electrode.
 17. A frequency filter comprising aMEMS resonator, the MEMS resonator having: an input electrode forinputting a signal; an output electrode for outputting a signal; and anoscillator facing the input electrode and the output electrode via aspace, the frequency filter characterized in that a balanced signal isinput to the input electrode and a balanced signal is output from theoutput electrode.
 18. The frequency filter according to claim 17,characterized in that: the input electrode includes a first inputelectrode and a second input electrode; the output electrode includes afirst output electrode and a second output electrode; the first inputelectrode and the first output electrode are disposed in such a mannerthat amplitude phases of the oscillator at positions of the first inputelectrode and the first output electrode become a same phase; and thesecond input electrode and the second output electrode are disposed insuch a manner that amplitude phases of the oscillator at positions ofthe second input electrode and the second output electrode become a samephase and different by 180° from the phase of the oscillator.
 19. Amanufacture method for a MEMS resonator, the MEMS resonator having: aninput electrode for inputting a signal; an output electrode foroutputting a signal; and an oscillator facing the input electrode andthe output electrode via a space, the manufacture method characterizedby comprising the steps of: forming the input electrode and the outputelectrode at the same time; forming a first input electrode and a secondinput electrode as the input electrodes; forming a first outputelectrode and a second output electrode as the output electrodes;disposing the first input electrode and the first output electrode insuch a manner that amplitude phases of the oscillator at positions ofthe first input electrode and the first output electrode become a samephase; and disposing the second input electrode and the second outputelectrode in such a manner that amplitude phases of the oscillator atpositions of the second input electrode and the second output electrodebecome a same phase and different by 180° from the phase of theoscillator.